Breast cancer incidence among women of Japanese ancestry living in the United States is three to four times higher than among women in Japan. Mammographic density patterns, which refer to the distribution of fat, connective, and epithelial tissue in the healthy female breast, are related to breast cancer risk. Therefore, we propose that Japanese women in Hawaii are more likely to have a dense parenchymal pattern than women in Japan. Reproductive and dietary factors may explain the differences in mammographic patterns. The purpose of the proposed pilot project is to standardize data collection procedures and to plan a comparative case-control study exploring the relative importance of mammographic densities and dit, in particular soy foods, as risk factors for breast cancer among women in Japan and women of Japanese and other ancestries living in Hawaii. The specific aims of this project are: 1. To develop common data collection procedures for diet and mammographic densities in densities in Hawaii and Japan. 2. To collect preliminary data on mammographic densities and diet among Japanese women. 3. To compare mammographic density patterns mammographic density patterns among women and children of Japanese ancestry in Hawaii. 4. To validate dietary soy assessment among women in Japan using urinary isoflavone excretion. As a planning tool, we propose a two-year cross-sectional study in Japan modeled after an ongoing study in Hawaii. We will recruit 200 asymptomatic women who received a mammogram at one of the two participating mammography clinical in Japan. Women whose mammogram did not have suspicious lesions will be contracted by mail and asked to complete a dietary questionnaire. Regular intake of soy, macro- and micronutrients including isoflavones will be estimated using a nutritional data base. Mammograms for all study participants will be sent to Hawaii. Mammographic densities will be assessed using a computerized quantitative method. Half of the participating women will be asked for an overnight urine sample which will be mailed to Hawaii and analyzed for isoflavonoids. During the statistical analysis, mammographic density patterns, dietary intake of isoflavones and other nutrients, and urinary isoflavone excretion patterns will be compared to information that has been collected in Hawaii during the last two years. This information will be used to develop the research plan and to estimate sample size for a collaborative case-control study.